General processes for fabricating semiconductor packages e.g. BGA semiconductor packages, include substrate loading, baking (at 120° C. for 1 hour), die bonding, curing (at 175° C. for 2 hours) and plasma cleaning etc, whereby plasma-cleaned substrates free of contaminant can be readily subjected to subsequent wire bonding and molding processes. This allows bonding wires and encapsulants to be formed on contamination-free substrates, and quality of packaged products can be assured. However, in practice, usually due to artificial errors or other reasons, some substrates are accidentally not cleaned by plasma, but directly used in the wire bonding and molding processes. These substrates inherent with contaminant may suffer quality degradation of wire bonding or electrical connection, and delamination would easily occur at interfaces between encapsulants and the contaminated substrates, making production yield of fabricated packages hardly improved.
Referring to FIG. 4, U.S. Pat. No. 6,068,129 discloses the forming of an indicator for indicating adhesion between an encapsulant and a substrate of a packaged electronic device. This indicator 11 is formed on a mold gate or runner 10 of the substrate 1, and made of solder mask that is also applied over other area on the substrate 1. Adhesion between the indicator 11 and the encapsulant (not shown) formed on the substrate 1 is good; while area of the mold gate 10 other than the indicator 11 is electrically plated with gold or palladium, making adhesion between the mold gate 10 and the encapsulant relatively poor. After the encapsulant is formed on the substrate 1, resin residues are usually remained on the mold gate 10 and need to be stripped off (customarily referred to as a degating process). During the degating process, if solder mask of the indicator 11 is entirely removed together with the resin residues, it indicates good adhesion between the substrate 1 and the encapsulant; on the other hand, if the indicator 11 is partly left on the mold gate 10, the encapsulant is proved not to be strongly bonded to the substrate 1, and delamination between the encapsulant and the substrate 1 may easily occur. Therefore, the provision of the indicator 11 allows packaged substrates firmly bonded with encapsulants to be selected and subsequently used for completing the fabrication of semiconductor packages.
However, the foregoing method for indicating adhesion between an encapsulant and a substrate has significant drawbacks. For example, this adhesion indicating method is carried out after forming the encapsulant, but not able to timely determine if the substrate is cleaned or contaminated before wire bonding and molding processes. As a result, packaged substrates not in good adhesion with encapsulants can only be discarded, which leads to considerable increase in material waste and costs, and also deterioration of fabrication productivity.
Therefore, how to promptly determine the cleanness of substrates before wire bonding and/or molding processes, and to assure bonding quality of bonding wires and encapsulants formed on the substrates, is a critical problem to solve.